What am I missing on the initialization of PIC16F877?

[kyru27]

I'm trying to control a pulse counter with a PIC and I'm having problems with the initialization, the code is:

BANKSEL ADCON1

MOVLW 0x0F
MOVWF ADCON1
MOVLW 0x10
MOVWF TRISA
MOVLW 0x00
MOVWF TRISB

BANKSEL PORTA

MOVLW 0x3F

MOVWF PORTB

But whatever I put on PORTB (wich is intended to send a "0" to a digit display) I always get a 0xFF, (so a 8 into display) in fact, all pins of the PIC are on High level. I guess I must be forgetting something as the Pic doesn't seem to be broken, I can read and program it without any issue, so the problema hast to be another one.

Can someone please help me with this? I'd be really grateful.

Thanks.

 

[Ian Rogers]

Show us your circuit... Have you current limiting resistors on port b? Is it acommon anode or common cathode digit display?

 

[kyru27]

I've resitors, they are at each exit of the PORTB and they illuminate all the displaay segments, it's a common cathode display.

I'm bringing 5 V to its corresponding pins , GND to their corresponding pins and so I guess it has to be the code, I guess just with VDD and GND set I should be measuring a 0x3F at PORTB wit a multimeter wheter I have resistors or display.

Thanks.

 

[Ian Rogers]

Same code works on simulation...

I don't know if you assembled with MPASM but here's what I did

	list p= 16f877
	#include "p16f877.inc"

loop	equ	20h
	org 	0
	goto	init

init
	BANKSEL ADCON1
	MOVLW 	0x0F
	MOVWF 	ADCON1
	MOVLW 	0x10
	MOVWF 	TRISA
	MOVLW 	0x00
	MOVWF 	TRISB
	BANKSEL PORTA

	MOVLW	0x3F
	MOVWF	loop
	MOVF	loop,W
	MOVWF 	PORTB
	DECFSZ	loop,F
	goto	$ - 3	
END

 

[kyru27]

Guess I'll give it a try, I don't think a loop should be necessary to initialize the PIC, but if it works that way...

Thanks.

 

[Ian Rogers]

Have you tied the MCLR to Vdd?

 

[kyru27]

Yes. 5 Volts all the time being sent there... Guess I'll try to redo the circuit from the beginning if someone can tell me that nothing more is neccesary to configure properly the ports.

 

[Ian Rogers]

Apart from the loop (I did this so could see a changing byte on the portb pins.) the code is fine..